Local and remote climatic drivers of extreme summer temperatures in the Arabian Gulf

Lachkar, Zouhair; Pauluis, Olivier; Paparella, Francesco; Khan, Basit; Burt, John A.

doi:https://doi.org/10.5194/egusphere-2025-2948

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https://doi.org/10.5194/egusphere-2025-2948

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07 Jul 2025

| 07 Jul 2025

Local and remote climatic drivers of extreme summer temperatures in the Arabian Gulf

Zouhair Lachkar, Olivier Pauluis, Francesco Paparella, Basit Khan, and John A. Burt

Abstract. The Arabian Gulf (also known as the Persian Gulf; hereafter simply the Gulf) is a shallow, subtropical, semi-enclosed sea that experiences the highest average summer sea surface temperatures (SSTs) in the global ocean. While local marine organisms have adapted to these extreme conditions, interannual temperature fluctuations result in occasional marine heatwaves that trigger mass coral bleaching and other ecological impacts. However, the climatic drivers of this variability remain poorly understood. In this study, we investigate the sources and mechanisms behind extreme summer temperatures in the Gulf. Analyzing a regional eddy-resolving ocean hindcast simulation combined with ERA5 reanalysis data, we find that extreme summer surface temperatures are tightly linked to lower-than-normal surface pressure over the Arabian Peninsula and higher-than-normal surface pressure over Iran and Pakistan. These pressure anomalies are typically associated with stronger monsoonal winds in the western Arabian Sea and weakened local winds. Enhanced monsoon circulation leads to (i) increased evaporation over the Arabian Sea and greater moisture transport into the Gulf in the lower troposphere, trapping heat near the surface, and (ii) enhanced subsidence over the Arabian Peninsula and the Gulf in the upper troposphere, inducing further surface heat retention. Meanwhile, weakened local Shamal winds – particularly in the northern Gulf – reduce evaporative cooling and facilitate the accumulation of moist, warm air, amplifying local warming. These regional atmospheric changes are strongly modulated by large-scale climate variability modes, with El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) together explaining over 50 % of the observed interannual SST variability in the Gulf. La Niña (El Niño) and the negative (positive) phase of the NAO both favor weaker (stronger) Shamal winds and warmer (cooler) SSTs during the peak summer months over the Gulf. Additionally, La Niña (El Niño) is associated with stronger (weaker) monsoon winds in the southern and western Arabian Sea, leading to stronger and more persistent warming (cooling) anomalies in the Gulf. The influence of these teleconnections is additive, with the warmest summers occurring when La Niña and negative NAO phases coincide. These findings have implications for the predictability of summer marine heatwaves and associated ecosystem risks in the Gulf.

Received: 20 Jun 2025 – Discussion started: 07 Jul 2025

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Zouhair Lachkar, Olivier Pauluis, Francesco Paparella, Basit Khan, and John A. Burt

Status: final response (author comments only)

RC1: 'Comment on egusphere-2025-2948', Anonymous Referee #1, 17 Jul 2025

Comments:
This study examines sea surface temperature (SST) variability in the Persian Gulf and its relationship with large-scale climate patterns (ENSO, NAO and IOD).
climate patterns (ENSO, NAO and IOD). The authors indicated that local atmospheric anomalies significantly impact SSTs in the Gulf by modulating heat fluxes. ENSO, NAO and IOD could impact SSTs in the Gulf by modulating the local atmosphere.
circulation. The combined effect of ENSO and NAO on SSTs in the Gulf is also discussed. The results obtained in this study are interesting. This manuscript can be accepted after revisions.

To confirm the results obtained from the ERA5, the authors should use other reanalysis data (e.g. MERRA2 and JRA55).

It should be noted that ENSO, IOD and NAO are not independent of each other. For instance, ENSO can affect IOD, IOD can affect ENSO, and NAO can also affect ENSO. The authors should examine the combined and relative effects of ENSO, IOD and NAO on SSTs in the Gulf using partial composite or regression analysis.

In addition to ENSO and the NAO, I would suggest that the authors also examine the role of Arctic sea ice anomalies in shaping extreme temperatures in the Gulf. Recent studies have indicated that Arctic sea ice anomalies could have a significant impact on ENSO, NAO and IOD. I suggest add some discussions. (https://doi.org/10.1175/JCLI-D-24-0419.1.; https://doi.org/10.1038/s41612-025-00936-x.; https://doi.org/10.1175/JCLI-D-23-0733.1.).

In addition to atmospheric heat fluxes, the tendency of SST should also be significantly impacted by oceanic dynamics, such as advection and upwelling/downwelling. The authors should analyse the SST tendency equation and investigate the role of these oceanic processes.

The authors discussed the possible influence of ENSO, NAO and IOD on SST anomalies in the Gulf. However, the underlying physical mechanisms have not been investigated in detail. The authors should examine the physical processes through which ENSO and NAO impact the formation of local atmospheric circulation. For example, Cheng et al. (2023; https://doi.org/10.1007/s00382-022-06616-3) indicated that AO/NAO-related atmospheric heating over the North Atlantic could trigger an atmospheric wave train from the North Atlantic to the northern Indian Ocean.

Citation: https://doi.org/10.5194/egusphere-2025-2948-RC1
RC2: 'Comment on egusphere-2025-2948', Anonymous Referee #2, 03 Sep 2025

The manuscript by Lachkar et al. addresses an important and timely topic by discussing the drivers of extreme summer sea surface temperatures in the Arabian Gulf. The authors combine an eddy-resolving ocean hindcast with ERA5 reanalysis, providing a framework to separate local and remote atmospheric influences. The work is well-motivated, as the Gulf is a critical hotspot of marine heat stress, with major ecological and socio-economic consequences. The manuscript is generally well-structured, the figures are clear, and the results are presented in a way that advances understanding of both local mechanisms (heat fluxes, Shamal winds) and large-scale teleconnections (ENSO, NAO). The finding that ENSO and NAO together explain over 50% of Gulf SST variability is particularly noteworthy and of interest for predictability. Overall, the paper makes a valuable contribution and is suitable for publication after some clarifications and refinements.
Specific Comments
The current manuscript however distinguishes itself from earlier studies by focusing on summer SST extremes and their mechanistic links to atmospheric circulation, but the introduction could better highlight how this work fills the gap left by earlier Gulf studies that relied on multi-seasonal or coarser analyses. Also, how the Arabian gulf understanding can be important for precipitation extreme changes having said that arabian gulf as one of the moisture source for heavy rainfall (can be seen in Pathak et al. 2025).
Pathak, R., Dasari, H.P., Ashok, K. et al. Dynamics of intensification of extreme precipitation events over the Arabian Peninsula derived from CMIP6 simulations. npj Clim Atmos Sci 8, 126 (2025). https://doi.org/10.1038/s41612-025-01016-w

It is interesting to see that ENSO and NAO act largely independently and additively is interesting. Would be interesting to have a discussion expanded to compare with other ocean basins, where ENSO–NAO interactions are sometimes nonlinear.

At LN170 and other places. The analysis finds a weak role for IOD and ISM. Given that the IOD is often invoked in regional SST variability, it would be helpful to provide a more explicit explanation of why its influence is muted in the Gulf, possibly due to the strong dominance of atmospheric fluxes over advective processes.

Please provide a schematic summarizing the coupled processes (weakening Shamal winds, enhanced subsidence, moisture build-up), and the same would be very useful for readers.
Since as we know that ENSO and NAO are routinely monitored, please provide lead time with which Gulf summer SST anomalies could be anticipated.

Citation: https://doi.org/10.5194/egusphere-2025-2948-RC2

Zouhair Lachkar, Olivier Pauluis, Francesco Paparella, Basit Khan, and John A. Burt

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Zouhair Lachkar, Olivier Pauluis, Francesco Paparella, Basit Khan, and John A. Burt

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Short summary

An analysis of model and reanalysis data reveals that extreme summer temperatures in the Arabian/Persian Gulf are driven by weakened local northwesterly Shamal winds and intensified monsoon winds over the Arabian Sea. These conditions – typically associated with La Niña and a negative NAO phase – increase air moisture over the Gulf and enhance surface heat trapping. The findings offer promising prospects for forecasting summer marine heatwaves in the Gulf and supporting mitigation efforts.


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